My original goal was a fairly modest one: $800, which would just cover the bare necessities of getting my book made, with a small buffer in case mistakes were made anywhere along the way. If my campaign had been funded exactly to the goal, I literally would have done all the art for free - certainly not a sustainable business plan for the long term.
Stretch goals inspire people to reach the next major milestone. They want to be the ones who put the total number into that next bracket. For that reason, set stretch goals close together.
My stretch goals were simple. For every $100 raised above my initial goal of $800, I would add an extra 5 illustrations to the book. From here out, I would begin to start earning money from the art I made. I used "Level Up!" as the cute catch phrase every time the "Amount pledged" number rose by another hundred. This was actually quite ambitious, seeing that I set myself on a strict timeline to finish the book by July. When the ideas were abundant, the bonus pieces were quick. But I did struggle here and there with minor bouts of creative block, especially as the 90th-95th pieces were being finalized.
As of the time of writing, Kickstarter currently does not have an in-system method to display or advertise stretch goals. Any stretch goal-ing you want to do must be done within the confines of their platform. Send out an email every few levels to remind your backers that they are getting some free stuff the more pledges you get.
3. Explain what the funds are used for.
People know they are contributing to your campaign with the hopes of supporting you. But, a lot of people have never done [whatever you are doing.] In my case, I know that people were curious about the costs of publishing a book - what are the steps? What does an ISBN do? You have to buy a barcode?
...and several other questions. Indulge their curiosity; explain the whole process. As best as possible, frame everything in the terms of adding value to the contributor. Tell them what you will be giving them back for their contribution.